1. Field of the Invention
The present general inventive concept relates to an image forming system, and more particularly, to a method and apparatus by which when a predetermined analog value is measured to control an image density or a high voltage output, a power source voltage variation due to change in a power line or a system variation is corrected such that the image density or the high voltage output can be precisely controlled.
2. Description of the Related Art
In an electrophotographic image forming system, when light corresponding to image information is scanned by an exposure unit on a photosensitive medium charged with a predetermined electric potential, an electrostatic latent image is formed on the photosensitive medium. A developer provides toner to the electrostatic latent image to form a toner image. Generally, in case of a color electrophotographic method, four developers containing cyan (C) toner, magenta (M) toner, yellow (Y) toner, and black (B) toner, are required. A formed toner image is transferred from the photosensitive medium to a paper directly or through an intermediate transfer medium. If the transferred toner image is passing through a fixer, the toner image is fixed on the paper by heat and pressure. Through this process, a monochrome image or a color image is printed on a paper.
Among methods for forming a color image, there are a single pass method and a multi pass method. In either case, the developing unit generally requires four developers as described above. Since the printing speed for a monochrome image is the same as that for a color image in the single pass method, the method has an advantage of high speed printing capability. In the multi pass method, printing a color image takes four times longer than printing a monochrome image in a simple calculation, but the multi pass method has an advantage that the structure of an apparatus based on this method is simpler than that based on the single pass method.
Among the kinds of high voltage required in this image forming system, there are, for example, a charge high voltage, a development high voltage, a first transfer high voltage, a second transfer high voltage, a cleaning high voltage, and a fusing high voltage. In order to maintain an optimal color image, a color image density sensor formed with a light emitting device and a light receiving device around a transfer belt is disposed, and according to the output of the color image density sensor, the level of a high voltage output such as the charge high voltage, the first transfer high voltage, and the second transfer high voltage, etc., is controlled. However, generally, in order to sense an image density in the color image density sensor, for example, a 5V power source voltage is used, and in order to analog-to-digitally convert the output of the color image density sensor, for example, a 3.3V power source voltage is used. Also, in order to recognize the environment of an image forming system, a detection value for environment recognition is measured at a predetermined cycle after the image forming system begins operation. The detection value for environment recognition can be, for example, the roll resistance value of a charge roller, a first transfer roller, and a second transfer roller. The roll resistance value changes by factors such as aging of the system and internal temperature rising, and accordingly, the charge high voltage and the first and second transfer high voltages need to be adjusted. However, generally, in order to measure the roll resistance value, for example, a 5V power source voltage is used, and in order to analog-to-digitally convert the measured roll resistance value, for example, a 3.3V power source voltage is used.
Thus, when a color image density is sensed or an environment detection value is measured, by using a second power source voltage that is different from a first power source voltage used in analog-to-digital conversion, if the second power source voltage changes due to a change in the power line or a system variation, it becomes impossible to obtain an accurate color image density or environment detection value, and as a result, it becomes very difficult to precisely control a high voltage output and an image density.